Looking back (e.g. skimming through recorded plays), it appears I've played the wizard 5 times since the change. That's about as many times as I played the wizard before the change, mainly because playing the old wizard used to feel like cheating (or playing on "easy mode"). Notable differences: An Air (only) Wizard feels about on par with other mages in terms of spell book building - maybe still a little stronger that usual because Arcane + an elemental school is cheap, but at least you can't choose Water and have all the Dissolves/Crumbles/Surging Waves you want for nearly free. I think my current wizard books have around 65 spells compared to about 70 before the change. Compare to most other mages that have about 50-60 spells.
As for the Wizard's Tower, it's now much trickier to play. You have to actually think about what spells you want it to cast, and in what order, since those spells get used up just like for every other non-Wand non-Thoughtspore familiar. For instance, if I only have 2 Acid Balls in my new wizard book, I have to think about when I want my Tower to cast them, if at all, since they're a truly limited resource... e.g. do I want to save 1 to put on an Elemental Wand in case I find I need more than 2 of them? In other words, there are risks and non-trivial decisions to be made - which is a good thing!
Overall, the Wizard still feels like one of the strongest mages, but not nearly as overpowered as before and much more interesting to play.